The present invention relates generally to a mobile radio telephone network system and, in particular, to a method for establishing an optimal registration zone in a code division multiple access (CDMA) system.
In the IS-95 CDMA system, a mobile telecommunication system comprises a plurality of base transceiver stations (BTS) providing communication service and a plurality of mobile stations (MS) served therefrom.
A CDMA system currently in operation in South Korea further comprises base station controllers (BSC) for controlling the BTSs, a base station manager system (BSM) for managing the BSCs, a mobile switching center (MSC) for connecting the BTSs to a public switched telephone network (PSTN), and a home location register (HLR) connected to the MSC for managing the service state of the mobile stations.
The BTSs are connected to the conventional public switched telephone network (PSTN). Mobile stations (MS) within a cell establish a radio channel to communicate with a BTS serving that cell. A forward channel is established from a BTS to a mobile station and a reverse channel is established from a mobile station to a BTS.
A mobile station (MS) and a BTS communicate both voice and data via the forward and reverse traffic channels. On the forward link, IS-95 defines four logical channels: pilot, paging, sync and traffic channels. The channels, with the exception of the traffic channel, are collectively referred to as an overhead channel. Each BTS and mobile station (MS) determine whether to receive data from one another based on the pilot or paging channel transmitted as part of the overhead channel.
The number of frequencies to be assigned to each BTS is predetermined as a function of the system capability and each BTS uses the assigned frequencies as needed. An assigned frequency channel is referred to as a frequency assignment (FA). The CDMA system has several access channels per frequency assignment (PA) by differing codes such as frequency option and sequence. Access channels are considered a part of overhead.
FIG. 1 is a block diagram illustrating a network of a conventional digital communication system (DCS). As illustrated, the network has a plurality of base transceiver stations (BTS) 1, a plurality of base station controllers (BSC) 2, mobile switching centers (MSC) 5 and 6, each MSC having a database associated therewith 51 and 61, the databases for storing information about subscribers transmitted from the HLR, a home location register (HLR) 3 and a public switched telephone network (PSTN) 7.
FIG. 2 is a block diagram illustrating a network of a conventional personal communication service system (PCS). As illustrated, the network comprises a plurality of base transceiver stations (BTS) 1 for providing communication service to mobile stations 9, a plurality of base station controllers (BSC) 2 for controlling the BTSs, private communication exchange (PCX) 8 for connecting a call via the BSC 2, and a public switched telephone network (PSTN) 7 for connecting a plurality of PCXs.
In a two-way communication system, as exemplified by FIGS. 1 and 2, the coverage area is often divided into smaller regions or zones where each zone is a group of one or more cells (i.e., base stations) treated as a unit. Several parameters such as paging, location registration and handoff are used to establish a location registration zone in the mobile telecommunication system. Among these parameters, paging load and location registration are important. The paging load is generated by paging each subscriber from the network and the location registration is required when a subscriber moves.
Paging is a process by which a BSC calls a moving subscriber to deliver an incoming call. For effective paging, timely location registration is also required. Location registration is the process by which a mobile station makes its presence known to a base station (BTS) to facilitate call delivery.
When a roaming mobile station does not register its location, a BTS requires a large number of paging loads to page the mobile station. At the other extreme, when the mobile station frequently registers its location, the base station (BTS) requires a large number of registration loads with the coincident effect that the base station (BTS) reduces its paging load requirement by providing accurate location information to the mobile station.
Consequently, a need exists for setting an optimal balance between paging load and registration load in setting a location registration zone of mobile stations.
Prior art analog networks are negligibly affected by a paging load, in that analog networks establish a location registration zone as a mobile switching center unit independent from the paging load.
However, by contrast, mobile telecommunication networks incorporating CDMA network are required to establish a location registration zone in consideration of both the paging load and the registration load requirements. In a mobile telecommunication network incorporating code division multiple access (CDMA), subscriber count and telephone traffic per subscriber is higher in comparison with an analog network, and as such the paging load is higher in comparison with an analog network.
It is therefore an object of the present invention to provide a method for setting a location registration zone in consideration of the registration load and a paging load requirement in a code division multiple access network.
In a preferred embodiment of the present invention, a method for setting a location registration zone in a code division multiple access system comprises the steps of: calculating a paging load for a mobile station in a specific test area, calculating a registration load for a mobile station in said test area, calculating the summation of said calculated paging load and registration load and determining an optimal number of base transceiver stations required to minimize said calculated summation and setting a location registration zone corresponding to a coverage area defined by said optimal number of base station transceivers.